Commercially, the alkylation of isoparaffins has been catalyzed by acids such as sulfuric acid and hydrofluoric acid. Conjunct polymer (acid soluble oils, (ASO) also known as red oil) forms as a byproduct of the alkylation reaction, as well as other hydrocarbon reactions. When too much conjunct polymer is present, the acid catalyst loses its effectiveness. The acid must be replaced with stronger acid, or the conjunct polymer must be removed in order to reactivate the catalyst. With sulfuric acid as the catalyst, the ASO is burned, and with hydrofluoric acid, the hydrofluoric acid is distilled away from the ASO. Sulfuric acid and hydrofluoric acid are hazardous and corrosive, and their use in industrial processes requires a variety of environmental controls.
Recently, there has been a desire to replace the use of sulfuric acid and hydrofluoric acid with more environmentally friendly materials. One such solution utilizes acidic ionic liquids as catalysts in hydrocarbon conversion processes, such as alkylation, isomerization, disproportionation, reverse disproportionation, and oligomerization. The ionic liquid catalysts are more environmentally friendly and therefore, more desirable than the sulfuric acid and hydrofluoric acid.
However, just as with the sulfuric acid and hydrofluoric acid, conjunct polymers are byproducts of the hydrocarbon reactions using ionic liquids. The conjunct polymers form a complex with the ionic liquid catalyst. The ionic liquid catalyst loses its effectiveness over time as the amount of conjunct polymer increases. Over time, the ionic liquid catalyst must then either be replaced or regenerated. Since ionic liquids are typically relatively expensive, efficient and effective processes for regenerating the ionic liquid catalysts are desired.
One process for regenerating the spent ionic liquid catalyst involves reducing the amount of conjunct polymer from the ionic liquid catalyst by contacting the spent ionic liquid catalyst with hydrogen gas. The contacting of spent ionic liquid catalyst with hydrogen gas takes place either on the surface of solid hydrogenation catalyst or in absence of solid hydrogenation catalyst. In processes conducted in the absence of a solid hydrogenation catalyst, the spent ionic liquid is contacted with hydrogen with sufficient and efficient mixing such as agitating, baffling, stirring, shaking, bubbling or any other methods (or combinations thereof). In regeneration processes, a content of conjunct polymer in spent ionic liquid catalyst is reduced to produce a regenerated ionic liquid catalyst which is recycled back to reaction zone.
Due to the beneficial nature of utilizing ionic liquid catalyst in hydrocarbon conversion reactions, including alkylation reactions, there is an ongoing and continuous need for efficient and effective processes for regenerating spent ionic liquid catalyst.